Devices for coding images are all the more effective as they code images possessing reduced temporal or spatial entropy.
They are therefore often associated with image pre-processing devices in which the images are processed in such a way as to allow better coding.
The aim of a video pre-processing is above all to increase the performance of an associated coding system, and this may manifest itself in 2 ways: improve the quality of the coded/decoded image for identical throughput, or decrease the coding throughput for identical image quality.
However, certain processing operations tend to reduce the definition of the image in an overly visible manner; it is therefore beneficial to establish effective control of these processing operations so as to best avoid these drawbacks.
The customary procedures for controlling spatial filters are often of a general kind: the sequence of images to be processed is characterized in a global manner and the severity of the filters is adjusted as a function of the result.